Siblicide in Serengeti spotted hyenas: a long-term study of maternal input and cub survival

In the Serengeti National Park, Tanzania, large fluctuations of prey abundance alters the frequency at which spotted hyena (Crocuta crocuta) cubs are nursed and thus the total level of maternal input available to them. Maternal input is high when mothers feed on high densities of locally available migratory herbivores and low when mothers travel up to 70 km to forage. Using data from 19 cub cohorts on the incidence of siblicide (from monitoring the survival of 609 cubs in twin litters) and cub growth rates (from 195 cubs in twin litters) as a measure of maternal input, we demonstrate that the incidence of siblicide increased as average cohort growth rate declined. In total, there were 37 siblicides in 384 litters (9% of litters). When both cubs were alive, total maternal input in siblicidal litters was significantly lower than in non-siblicidal litters and the mean share of the dominant sib of 64.6% was significantly higher than the mean of 52.1% for dominant sibs of non-siblicidal litters. After siblicide, growth rates of siblicide victors substantially increased, demonstrating that mothers did not reduce maternal input after litter reduction. As a result, siblicide victors achieved a long-term growth rate similar to that of singletons and thus significantly increased their expected survival. We conclude that in spotted hyenas, high maternal input in lactation has favoured the evolution of facultative siblicide in populations inhabiting areas with low or fluctuating food resources.